1. Field of the Invention
The present invention relates to a method of and an apparatus for bending sheets of glass for use as a laminated sheet of glass.
2. Description of the Prior Art
Heretofore, it has been customary to form laminated sheets of glass for use as automobile front windshields or the like by conveying two sheets of glass on a ring mold through a furnace and preliminarily and then finally shaping the sheets of glass while they are in the furnace.
Various known apparatus for manufacturing such laminated glass sheets are disclosed in Japanese laid-open patent publications Nos. 63-156025, 1-230439, 2-38331, 2-38332, and 2-55240, for example. The apparatus shown in Japanese laid-open patent publication No. 63-156025 has a gravity bending zone and a press bending zone in a furnace. While sheets of glass are being conveyed on a ring mold through the furnace, they are first preliminarily shaped or bent by gravity in the gravity bending zone, and then finally shaped in the press bending zone by an upper mold which is lowered toward the ring mold. Thereafter, the bent sheets of glass are annealed on the ring mold. In the apparatus shown in Japanese laid-open patent publication No. 1-230439, a presser is mounted on a carrier on which a ring mold is supported, and an auxiliary press in a press bending zone is actuated to press opposite sides of glass sheets to shape between the ring mold and the presser. The apparatus disclosed in Japanese laid-open patent publication No. 2-38331 has two parallel furnaces, one for preliminarily shaping glass sheets and one for finally shaping glass sheets, and a feeder for feeding the glass sheets between these furnaces. Japanese laid-open patent publication No. 2-38332 discloses a heater disposed in an upper mold which cooperates with a ring mold in pressing glass sheets to shape in a press bending zone. According to the apparatus disclosed in Japanese laid-open patent publication No. 2-55240, sheets of glass are pressed to shape between an upper mold and a ring mold in a press bending zone, and then edge regions of the glass sheets are tempered with a special cooling mold.
In either one of the above conventional apparatus, the ring mold which has been used to convey or preliminarily bend the glass sheets is used again to finally bend the glass sheets in the press bending zone. Therefore, the ring mold is required to be rugged enough to withstand the pressure that is applied when the glass sheets are pressed to shape in the press bending zone. As a result, the ring mold is relatively heavy and a large expenditure of energy and time is needed to move the ring mold. The fact that the ring mold has a shape complementary to the shape of a final laminated glass sheet product makes the ring mold unsuitable for the preliminary shaping of glass sheets. Moreover, inasmuch as the ring mold doubles as a lower mold at the time the glass sheets are pressed to shape by the upper mold and also as a support for the glass sheets when they are conveyed, the upper mold has to be moved downwardly and upwardly for pressing the glass sheets. The requirement to lift and lower the upper mold results in a complex overall apparatus construction.